In modern internal combustion engines, camshaft adjusters are used in order to be able to variably configure the phase relationship between the crankshaft and camshaft in a defined angle range, between a maximum early position and a maximum late position. For this purpose, the camshaft adjuster is integrated into a drive train via which torque is transmitted to the camshaft by the crankshaft. Said drive train may be realized, for example, as a belt drive, chain drive or gearwheel drive. Camshaft adjusters of this type are generally designed as hydraulic oscillating motors, for example of vane cell design, with at least two pressure chambers acting in an opposed manner. The supply of pressure medium to or the removal of pressure medium from the pressure chambers is controlled by means of a hydraulic directional control valve, for example a proportional valve. Embodiments are known in this connection, in which the hydraulic directional control valve is arranged in a central passage opening of the camshaft adjuster and rotates together therewith. Directional control valves of this type are customarily referred to as central valves.
A central valve of this type is known, for example, from DE 10 2004 038 160 A1. In this embodiment, a camshaft of hollow design reaches through a central passage opening of the camshaft adjuster. Within the camshaft, the central valve is arranged in the region of the camshaft adjuster. The central valve consists of a valve housing, a control piston, a spring element and a snap ring. The valve housing, which is of substantially hollow-cylindrical design, has an inlet connection, an outlet connection and two working connections on the outer circumferential surface thereof. Furthermore, an axial outlet connection is provided. The inlet connection communicates with a pressure medium pump of the internal combustion engine, the outlet connections communicate with a pressure medium reservoir of the internal combustion engine, and the working connections each communicate with a group of pressure chambers of the camshaft adjuster. The control piston is arranged in an axially displaceable manner within the valve housing. In this case, the control piston is displaced into any position between two end stops and held there by means of an electromagnetic adjusting unit counter to the force of the spring element supported on the control piston and the valve housing. The first end stop is implemented by way of the snap ring which is arranged at the open end of the valve housing. The second end stop is implemented by way of the spring receptacle.
Depending on the position of the control piston relative to the valve housing, the volumetric flow of pressure medium fed by the pressure medium pump to the inlet connection is conducted to the first or second working connection and therefore to the first or the second pressure chambers. At the same time, the pressure medium is ejected from the other pressure chambers via the other working connection and one of the outlet connections into the pressure medium reservoir.
In addition to the hydraulic connections, the valve housing has a fastening section, a threaded section in the embodiment illustrated, by means of which the central valve is fixed within the camshaft. Furthermore, a collar which extends in the radial direction, protrudes over the camshaft in the radial direction and bears in the axial direction against a cylinder head of the internal combustion engine is formed on that section of the valve housing which projects out of the camshaft. The collar therefore constitutes part of the axial bearing of the camshaft relative to the cylinder head.
Via the axial bearing and the fastening section, a high amount of force is admitted to the valve housing which has to be of appropriately stable design. The valve housing is customarily produced from a metal blank by means of machining production processes.